Cogongrass (Imperata cylindrica) Affects Above- and Belowground Processes in Commercial Loblolly Pine (Pinus taeda) Stands

Cogongrass (Imperata cylindrica), an invasive grass species native to Asia, has been shown to reduce tree vigor in loblolly pine (Pinus taeda) plantations, which comprise more than 50% of growing stock in commercial forests of the United States. I. cylindrica produces exudates with possible allelopathic effects that may influence abundance of P. taeda symbionts, such as soil microbes and ectomycorrhizal fungi. Soil microbial communities and root colonization by mycorrhizal fungi were sampled in intensively managed P. taeda stands in Greene County, Mississippi, in I. cylindrica present and absent plots. I. cylindrica present plots had reduced abundance of ectomycorrhizal colonization of pine fine feeder roots in the top 40 cm of soil in comparison to I. cylindrica absent plots. Abundance of pine fine feeder roots in the 21–40 cm and 41–60 cm layers of the soil profile was also reduced in I. cylindrica present plots. Vegetative diversity was negatively correlated with I. cylindrica (% cover), which probably contributed to the reduced microbial diversity in I. cylindrica present plots. Because of the variety of roles microorganisms play, changes associated with the invasion of I. cylindrica are likely to alter nutrient cycling and reduce site productivity.